1. Field of the Invention
The present invention generally relates to a fan circuit, and more particularly to a fan circuit with a fan speed control circuit capable of being employed in different systems.
2. Description of Related Art
Nowadays, many electronic devices generate much heat during operation. Such heat can adversely affect operational stability of electronic devices. Accumulation of the heat in electronic devices can lead to high temperatures in the electronic devices, thus resulting in unstable operation and even destruction of the electronic devices. Therefore, the heat must be removed in time to keep the temperature of the electronic devices within a safe range. Fans have been used in the electronic devices for providing forced airflows to dissipate the heat. In order to effectively reduce vibrations and noises in a fan, the speed of the fan must be controlled. Among conventional fan speed control technologies, pulse width modulation (PWM) control is the most common method used to control the speed of the fan.
Referring to FIG. 3, a fan speed control circuit 70 in accordance with related art comprises a digital/analog converting unit 701 and a driving unit 702. The digital/analog converting unit 701 converts an inputted PWM digital signal 60 into an analog signal such as a voltage signal. A Hall element detects a magnetic polarity of a rotor in a fan (not shown), and gives output signal denoting magnetic pole positions of the rotor. The driving unit 702 receives the analog signal from the digital/analog converting unit 701 and the output signal of the Hall element 90. After that, a digital signal outputted from the driving unit 702 is used to control the terminal voltage of the stator coil 80 powering the fan, thus allowing the speed of the fan to be controlled.
However, characters of inputted PWM digital signals are different for different electronic devices and different systems. In conventional fan speed control circuit, the digital/analog converting unit must be changed if the fan is used in a different electronic device to receive different PWM digital signals, with other electronic elements of the fan circuit also needing to be changed. Therefore, if the fan is used in a different system, fan circuits installed with the fan speed control circuit must be redesigned, and the manufacturing cost of the fan will increase as a result.
Therefore, what is needed is a fan circuit having a fan speed control circuit capable of being employed in different systems without redesigning the fan circuit.